1. Field of Endeavor
The present invention relates to the field of combustion engineering, in particular in connection with gas turbines. It relates to a method for adjusting a Helmholtz resonator in and to an adjustable Helmholtz resonator.
2. Brief Description of the Related Art
The use of Helmholtz resonators for damping pulsations in the combustion chambers of gas turbines has already been proposed a number of times (see, for example, DE-B4-196 40 980). Helmholtz resonators with a plurality of resonator volumes connected one behind the other, with which multiple frequencies can be damped, have also already been disclosed (see, for example, DE-A1-10 2005 062 284).
The effectiveness of such damping systems is restricted to a narrow frequency range around the resonant frequency of the individual dampers. The damping characteristic of such systems is a function of the acoustic impedance of the constriction used to couple the respective resonator volume to the space to be provided with damping, in particular the combustion chamber of a gas turbine. The acoustic impedance of the constriction for its part is a function of the flow rate and the pressure loss coefficient in the constriction. For Helmholtz resonators with only one resonator volume, the resonant frequency is only weakly dependent on the acoustic impedance in the constriction. For two resonator volumes, however, the resonant frequency is highly dependent on this impedance.
In general, it is desirable to have a Helmholtz resonator which can be matched to the pulsations actually occurring in a combustion chamber in order to achieve the greatest possible damping effect. In the aforementioned DE-A1-10 2005 062 284, this can be achieved, for example, by virtue of the fact that an adjustable plunger is arranged in the resonator volume. Such a mechanical adjustment is complex in terms of construction, however, and is poorly suited to active regulation.